This glitch is the only way to access some of the Red/Blue glitch Pokémon's evolutions, such as ◣ゥ 8 (hex:C9)'s evolution via 'exposure to a Card Key' at at least level 28, into C (hex:E5).

The evolve without an evolutionary stone glitch is a glitch in Pokémon Red and Blue that allows the player to evolve a Pokémon without an evolutionary stone, or to access glitch Pokémon evolutions that would otherwise be impossible. It was fixed in Pokémon Yellow.

Directions

Have the first Pokémon in the player's party, the one he or she is trying to evolve, gain a level.

Switch out the Pokémon that the player is trying to evolve and put the Pokémon that corresponds to the necessary evolution stone.

Have that Pokémon finish the Trainer battle.

Additional information

This glitch can also be done when encountering a wild Pokémon. Have the Pokémon you're trying to evolve start the battle and then change Pokémon and place the Pokémon that corresponds to the required evolution stone in battle. Have the Pokémon end the battle. Both Pokémon will gain experience and for the glitch to work, the Pokémon the player is trying to evolve will need to gain a level from the experience it gains.

Evolving glitch Pokémon with this glitch

More research is needed for this article.

Reason given: Verify these evolutions.

Certain glitch Pokémon evolve by 'exposure to an item' that isn't an evolutionary stone. Others may evolve with a valid stone, but only through this glitch and not through the actual item. An example is the glitch Pokémon O PkMn4 X, which can evolve at level 6 or more when using this glitch with Exeggutor (corresponding to Moon Stone).

Here is a list of glitch Pokémon stone or item evolutions by echinodermata. Note that the data was taken from the ROM, so there may be some evolutions that do not work.